The present invention relates to the removal of organic contaminants, such as chloral, from aqueous HCl. The problems associated with the removal of chloral from aqueous HCl are well known to those skilled in the art.
Hydrogen chloride resulting from chlorination reactions, either as unreacted starting material or as a by-product of such reactions, often contains organic materials as undesirable contaminants. Since the hydrogen chloride (HCl) is generally recovered with water, the resulting aqueous hydrochloric acid typically contains such undesirable contaminants. For example, the oxychlorination of ethylene with oxygen and HCl over a copper-containing catalyst yields ethylene dichloride (EDC) and water with small amounts of organic contaminants, such as chloral and others such as ethylene chlorohydrin, ethanol, dichloracetaldehyde and the like, which must be removed from the water-EDC-unreacted HCl mixture for a variety of reasons well known in the art. While a variety of methods can be employed to remove chloral from the EDC, such as, for example, as noted in U.S. Pat. Nos. 3,378,597; 3,488,398 and 3,996,300, the remaining HCl ends up either neutralized with base or contaminated with chloral and other organic contaminants if absorbed out in water before the base wash. Aqeuous HCl solutions contaminated with chloral also result from the manufacture of chloral by aqueous phase chlorination of materials such as acetaldehyde, paraldehyde, alcohol or their partially chlorinated derivatives.
The removal of chloral from aqueous HCl by distillation at atmospheric pressure is taught in Japanese Pat. No. 49 83,694, wherein the distillation is carried out in a batch still. However, a large portion of the HCl feed must be distilled off to reduce the chloral level; for example, about 50% of the feed must be distilled off in 10% HCl to reduce the chloral level to about 80 ppm. Such method is disadvantageous in that a high energy input level is required and in that large amounts of the HCl feed are lost overhead. In U.S. Pat. No. 2,746,912, HCl gas is added to concentrated chloral-water mixtures in an amount sufficient to provide 1 part HCl to 4 parts of water and the mixture is continuously distilled. While substantially water-free chloral is obtained as the overhead, the 10-36% aqueous HCl bottoms are contaminated with up to about 12% by weight chloral. Distillation of aqueous solutions of chloral, mono- and dichloroacetaldehyde at 1-5 atmospheres to remove the chloracetaldehydes is taught in German Pat. No. 1,129,942 a substantially chlorine-free residue being thus obtained.